1. Field of the Invention
The present invention relates to an apparatus for forming an image which comprises a plurality of image carriers, a plurality of charging means for charging the respective image carriers, light beam generating means for generating a plurality of light beams to which the image carriers are exposed so that an electrostatic latent image is formed on each image carrier in accordance with image signals, and a plurality of developing agent supplying means for supplying a developing agent which develops the electrostatic latent images on the respective image carriers.
2. Description of the Related Art
An example of a conventional image forming apparatus of an electrophotographic printing type for forming a multi-color image on paper is disclosed in Japanese Unexamined Patent Publications JP-A 6-143686 (1994) and JP-A 8-160694 (1996), for example.
The former discloses a 3-level tandem printer which is a 4-color printer having a tandem structure in which three 3-level engines utilizing an adjacent spot technique for 3-level imaging are disposed. Each 3-level engine comprises a photoconductive drum which serves as a photosensitive member, a charging part for uniformly charging a surface of the photoconductive drum, and a scanning apparatus for exposing the charged surface of the photoconductive drum. The 3-level engines each comprise the scanning apparatus, and therefore, the 3-level tandem printer as a whole requires to comprise three scanning apparatuses whose structures are independent of each other. Accordingly the number of parts and components which constitute the printer increases, resulting in an upsized printer. In particular, each scanning apparatus tends to require a large number of parts and components because it is composed of an optical device, a sensor, a laser, and a resident control device, and hence, a large installment space is required, which in turn increases the size of the printer.
Meanwhile, the image forming apparatus disclosed in JP-A 8-160694 comprises a control part for outputting image signals for yellow, magenta and cyan with delay by different time intervals, a laser diode for receiving the image signals and converting the image signals into yellow, magenta and cyan optical signals, a polygon mirror, which includes yellow, magenta and cyan reflection surfaces which correspond respectively to the optical signals and have different inclination angles from each other, for receiving the optical signals from the laser diode at the reflection surfaces while rotating and reflecting the optical signals respectively in three directions which are at different angles from each other, yellow, magenta and cyan converging lenses, which are disposed on optical paths of the respective optical signals which are reflected by the polygon mirror, for receiving and converging the respective optical signals, yellow, magenta and cyan reflection mirrors for respectively reflecting the optical signal which passed the respective converging lenses, and yellow, magenta and cyan photoconductive drums which are disposed in correspondence with the respective reflection mirrors to be exposed to the respective optical signals which are reflected by the respective reflection mirrors.
In the image forming apparatus which has such a structure described above, since yellow, magenta and cyan laser light beams from the laser diode are reflected by the polygon mirror at the reflection surfaces of different inclination angles from each other in the three directions, in order to reflect each laser light beam at the associated photoconductive drum, the three reflection mirrors for yellow, magenta and cyan are necessary, and therefore, it is necessary to use an increased number of parts and components and ensure spaces for disposing the three reflection mirrors, which in turn increases the size of the main body of the image forming apparatus.